core: AMCREST Camera component: Empty camera sdcard throws error

Version HASSIO 84.6

        "hostname": "hassio",
        "operating_system": "HassOS 1.13",
        "deployment": "production",
        "kernel": "4.14.81-v7"

Environment Hassio on RasPi3 B+ | Amcrest IP cameras with sdcard support

Amcrest component

Description of problem: If a new SDCard is installed (or not present) the logic for reporting the SDCard disk usage throws an index error in storage.py and no sensor entity is created.

Problem-relevant configuration.yaml entries and (fill out even if it seems unimportant):

amcrest:
  - host: 192.168.xxx.xxx
    name: "xxx"
    username: userid
    password: !secret ipc_pw
    resolution: high
    stream_source: rtsp
    port: 80
    sensors:
      - ptz_preset
      - sdcard
  - host: 192.168.xxx.xxx
    name: "yyy"
    username: userid
    password: !secret ipc_pw
    resolution: high
    stream_source: rtsp
    port: 80
    sensors:
      - sdcard

Traceback (if applicable):

2019-01-11 08:27:25 ERROR (MainThread) [homeassistant.components.sensor] amcrest: Error on device update!
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/homeassistant/helpers/entity_platform.py", line 248, in _async_add_entity
    await entity.async_device_update(warning=False)
  File "/usr/local/lib/python3.6/site-packages/homeassistant/helpers/entity.py", line 349, in async_device_update
    await self.hass.async_add_executor_job(self.update)
  File "/usr/local/lib/python3.6/concurrent/futures/thread.py", line 56, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/usr/local/lib/python3.6/site-packages/homeassistant/components/sensor/amcrest.py", line 103, in update
    sd_used = self._camera.storage_used
  File "/usr/local/lib/python3.6/site-packages/amcrest/storage.py", line 39, in storage_used
    status = [s for s in ret.split() if '.UsedBytes=' in s][0]
IndexError: list index out of range

Additional information: I’m actually now using @pnbruckner customized amcrest component which I see is in the process of being merged into the official component. I believe this error was present in the original component as well. In any case, it is a very minor issue since when data is written to the card, the error should go away.